How did the packaging/debian subdirectory originally come to be?
The idea was that since the Debian packages of Pike broke much Pike functionality and we (upstream Pike developers) knew and saw so little of what happened when with the Debian Pike port, except feedback from Debian users that ended up with us instead of in the Debian package's bug reports where they are supposed to go,
(...dang, I'm stuck in endless sentence mode! ...oh, well.)
...we invited the code to live directly in the Pike codebase, where it would at least be visible to us, even if the Debian maintainer's decisions on packaging were still final (I think people tried to help point out patches that prevented Debian's pike from building external modules, but stopped, when there was little action to re-enable that).
There is some info in packaging/README too about these things, without going into that level of detail on the history that led to the present repository layout (no need spilling reader time on past events). It proved a good idea, and other package systems were invited with open arms too, so we now have fink there as well. It was also the natural spot to put the rather exotic Windows build procedure, once devised.